Mine firing control apparatus

ABSTRACT

1. In a submarine mine for damaging a vessel, the combination of: a mine, electrical means responsive to a condition having a variable sign and caused by a vessel in motion for producing signals of opposite polarities in accordance with the sign of said condition, a pair of energy storage means, means controlled by said signals for selectively supplying said energy storage means with energy in accordance with the polarities of said signals, and means controlled by one of said energy storage means for firing the mine when the pair of energy storage means are successively supplied with energy within a predetermined period of time.

[451 Mar. 27, 1973 803,907 7/1936 France [54] MINE FIRING CONTROL APPARATUS [75 Inventors: Ralph W. Mann; Frank B. Johnson,

Primary Examiner-S. W. Engle both of Washington, DC.

Assignee: The United States of America as Att0rneyG. J. Rubens et a1.

represented by the Secretary of the EXEMPLARY CLAlM Nav y 1. In a submarine mine for damaging a vessel, the combination of: a mine, electrical means responsive to Aug. 28, 1943 [21] App]. No.: 3,983

[22] Filed:

a condition having a variable sign and caused by a vessel in motion for producing signals of opposite polarities in accordance with the sign of said condition, a

pair, of energy storage means, means controlled by said signals for selectively supplying said energy storage means with energy in accordance with the polarities of said signals, and means controlled by one of said energy storage means for firing the mine when v UNITED STATES PATENTS the pair of energy storage meansare successively supplied with energy within a predetermined period of time.

22 Claims, 2 Drawing Figures I Duffie 1/1921 Da Cruz.. 5/1925 FOREIGN PATENTS OR APPLICATIONS 117,603 10/1943 Australia.....................'........102/702 Ms 5 A PATEI'HEURARZYISYS I 722 409 SHEET 2 BF 2 Flag, 2.

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4 film 1 R.WMann Eli. Johnson MINE FIRING CONTROL APPARATUS v This invention relates to firing control apparatus for submarine mines and more particularly to a firing control apparatus in which a plurality of electronic tube networks are selectively controlled in predetermined time relation in response to signals received throu the water by a signal detecting device.

In certain types of mines, it is the practice to cause the mine firing mechanism to respond to a signal induced by a particular one of the phenomena associated with the vessel in motion when the vessel is in the vicinity of the mine, such response of the mine being effective after a predetermined period of time to arm the mine or place it in condition to receive a second signal induced by said one of the phenomena. In the event that the second signal is received within a predetermined period of time after the mine has been armed, the mine is exploded. However, if the second signal is not received during the period in which the mine remains armed, the mine firing control mechanism is restored to normal without fii'ing the mine.

In firing control mechanisms heretofore proposed for controlling the firing of a mine in the manner described hereinabove, it has been the usual practice to employ time measuring devices comprising mechanical elements such as switches operated by step-by-step motors, rotary motors, clock movements, escapement devices, dashpots and the like. Such time measuring devices have not proved altogether satisfactory in service for the reason-that mechanical devices, because of the relatively large mass of the elements and the necessity of employing moving parts therein, are particularly susceptible to damage or injury thereto as the result of the shock or blow which the time measuring device receives-at the moment the mine in which it is mounted strikes the water or the bed of the sea at the time of planting of the mine. Such shocksare' particularly intense in the case wherejthe mine is launched from an aircraft in flight and various expedients, such as attaching a parachute to the mine or dropping of the mine from a low altitude, have been resorted to in order to reduce the shock to a value which will not damage the mine firing control mechanism.

In the arrangement of the present invention, these difficulties are avoided by the employment in the firing control apparatus fora mine of electrical timing networks comprised of very'light elements ruggedly constructed and having no moving parts in place of those portions of the prior mechanisms which were most susceptible to-shock. More specifically, the mine firing control apparatus of the present invention comprises a coil in which are induced electrical currents of opposite polarity when the magneticfield adjacent the mine is disturbed by the passage of a vessel in the vicinity thereof, such disturbance of the field being hereinafter referred to as the magnetic signatureof the vessehlt is known that the magnetic signature varies'underdifferent portions of a vessel in both direction and intensity and the currents induced in the coil will therefore change in polarity and magnitude in accordance with the magnetic signature of the vessel. This variation in direction is referred to herein as the polarity of the magnetic field.

The coil is connected to a sensitive galvanometer type of instrument which causes energization of a pair of circuits selectively in accordance with the polarity of the current induced-in the coil. Each circuit has connected therein an electrical network including a condenser in series with a resistor both of which are connected in parallel with a series circuit including a detonator and the plate circuit of a cold cathode tube. The networks are so interconnected that the charge on the condenser in one network, when that network is momentarily energized, maintains the grid of the cold cathode tube which has its plate circuit connected in the other network at firing potential for a predetermined period of time so that energization of the latter network during said predetermined period will fire the cold cathode tube and ignite the detonator thereby causing the mine to explode. In the event that energization of the latter network does not occur within said predetermined period, the charge on the condenser leaks off through the grid circuit until the grid potential is below the firing value and the tube is rendered nonresponsive to energization of the network in which its plate circuit is connected.

It is, therefore, apparent from the preceding description that the mine firing control apparatus of the present invention requires a reversal within a predetermined period of time in the direction of the magnetic field disturbance caused by a vessel before the firing control means will operate to explode the mine whereby sweeping of the mine by the present known methods is rendered more difficult'.

The mine firing-control apparatus of the present invention is also provided with electronic means for preventing countermine shocks from causing the apparatus to fire in response thereto thus precluding the destruction of the mine by deliberate explosions caused by the enemy or by the explosion of adjacent mines.

One'of the objects of the present invention is the provision of a new and improved mine firing control apparatus. in which the foregoing disadvantages are obviated and which possesses all of the advantages of arrangements heretofore proposed for this purpose.

Another object of the invention is to provide a mine firing control apparatus in which electrical networks having no moving parts are employed for measuring various time periods.

' An additional object of the invention resides in a novel and improved arrangement whereby cold cathode tubes are employed in a mine firing control circuit thereby to reduce the drain on the mine batteries to a minimum.

A further object of the present invention is to provide a mine firing control circuit in which electrical tion taken in connection with the accompanying drawings in which:

FIG. 1 is a view insection of a mine suitable for use with the mine firing control circuit of the present invention; and

FIG. 2 illustrates in diagrammatic form a complete circuit suitable for use with the mine of FIG. 1 according to a preferred embodiment of the invention.

Referring now to the drawings in which like numerals of reference are employed to designate like parts throughout the several views, there is shown in FIG. 1 a mine indicated generally by the numeral having a casing 11 adapted to be sealed by a cap or cover 12 secured thereto as by the bolts 13, a gasket 14 being preferably arranged between the cover and the casing to insure a watertight joint therebetween. There is arranged within the casing 11, a wall or partition 15 welded or otherwise secured to the casing 11 and provided with a well 16 for a purpose to be hereinafter disclosed.

Secured on the exterior of the well 16 is an annular support 17 adapted to receive one end of an induction pickup coil 18 comprising a relatively large number of turns of wire 19 arranged about a rod 21 of iron or composed of a material sold under the trade name of Permalloy, the rod and wire being enclosed in a sup porting and protective sheath 22. The other end of the coil is disposed within a recessed porfion 23 of the casing 11, suitable pads or cushions 24 being arranged between the ends of the coil and recessed portion 23 and support 17 respectively to prevent damage or injury to the coil as the mine is launched.

The partition 15 also forms a chamber 25 within which is arranged an explosive charge 26 of TNT or the like sufficient to destroy or damage a vessel and to impart a negative degree of buoyancy to the mine whereby the mine is adapted to come to rest on the bed of a body of water after being launched therein. A suitable watertight filler opening is provided by means of which the charge 26 is introduced within the mine casing.

There is also provided within the chamber a well 27 within which is arranged an explosive booster charge 28 as is well known in the art to which the invention pertains. There is also arranged within the well 27 a hydrostat mechanism comprising a plunger or rod 29 slideably arranged within the support 31 and normally urged outwardly therefrom by a spring 32 in engagement with the collar 33 secured to the plunger. A flexible diaphragm 34 is clamped to the collar 33 as by the nut 35, the diaphragm being maintained in watertight relation with respect to the well 27 as by the bolts 36 and a clamping ring 37. A soluble washer 38 secured to the plunger as by the nut 39 prevents the inward movement of the plunger until the mine has been planted for a period of time suflicient to dissolve or soften the soluble washer. When this occurs, the detonating device 41 is moved by the plunger into operative relation with respect to the booster charge 26. The detonating device 41 is connected electrically by means of a pair of conductors which pass through a duct 42 to the various other components of the mine mechanism.

The mine is also provided with a recess or well 43 within which is arranged a hydrostat 44 adapted to set an arming clock 45 into operation in response to the movement of the hydrostat under the influence of the surrounding water. The arming clock may be of any type suitable for the purpose adapted to close circuits between a plurality of pairs of conductors within the duct 46 and connected to the other components of the mine mechanism as will hereinafter be described. A suitable arming clock is described and claimed in the copending application of James B. Glennon et al for Firing Mechanism For A Submarine Mine, Ser. No. 395, 230, filed May 26, 1941.

The mine firing mechanism comprises a signal amplifying device indicated generally by the numeral 47 arranged preferably within a suitable resilient cushion or pad 48 fitted within the mine case in abutting relation with the partition 15 and the cap 12, a battery 49 within the well 16 being provided for the operation of the mine firing control mechanism. The battery 49 is preferably disposed within a suitable pad 51 of yieldable material, the pads 48 and 51 which are composed of rubber or the like being for the purpose of preventing injury to the amplifying device or the battery respectively when the mine is launched. A plurality of fins 52 secured to the mine casing 11 in any suitable manner are employed to direct and steer the mine during the launching thereof within a body of water. The pad 48 is provided with an aperture 53 therein within which is arranged the electrical cable 54 for establishing an external electrical connection from the device 47 to the other components of the mine.

Referring now to FIG. 2 of the drawings, the circuit connections extending between the various elements of the mine firing mechanism are diagrammatically illustrated therein. The induction pickup coil 18, hereinafter referred to as a search coil, is electrically connected by the leads 55 to the moving coil 56 of a polarized relay 57, known in the art as a Sensitrol relay, the relay 57 being also provided with a reset coil 58 for retuming the relay armature 59 to its neutral position between the relay contacts 61 and 62 which are composed of magnetic material and tend therefore to maintain the armature 59in contact therewith after the coil 56 has once been energized. Engagement of the contact 61 by the armature 59 energizes a telephone type relay 63 having a coil 64, a resistor 65 being in series with the coil 64 and a condenser 66 being connected in parallel with the coil 64 and resistor 65 to produce a time delay in the energization and deenergization of the coil. The relay 63 is provided with an armature 67 normally out of contact with a contact 68 and an armature 69 normally out of contact with a contact 71. The armature 59 of the relay 57, when it engages the contact 62, energizes a telephone type relay 72 provided with a coil 73, arrnatures 74 and 75, normally open contacts 76 and 77, a resistor 78 and a condenser 79 all arranged in the same manner as the elements of the relay 63.

The arming clock 45 is provided, as disclosed in the aforesaid application of James B. Glennon et al, with three sets of contacts 81, 82 and 83 operated by a spring and escapement driven cam 84, the cam being so arranged that the contacts 81 close in one hour after the clock has been started, the contacts 82 close in two hours and the contacts 83 close in three hours to energize various parts of the circuit from the battery 49 which is shunted by a condenser 85 for a purpose to b disclosed hereinafter.

The relay 63, when energized, closes a circuit to charge a condenser 86 through a resistor 87, the detonator 41 and a cold cathode tube 88 being connected in series across the condenser 86 and resistor 8'7. Upon energization the relay 72, in a manner similar to relay 63, closes a circuit to charge a condenser 89 through a resistor 91, a series circuit including the cold cathode tube 92 and the detonator 41 being connected in parallel with the condenser 89 and the resistor 91. The grid 93 of the tube 92 is connected through a grid resistor 94 to the point 95 between the condenser 86 and the resistor 87 and the grid 96 of the tube 88 is similarly connected through the grid resistor 97 to the point 98 between the condenser 89 and the resistor 91.

As will more clearly appear as the description proceeds, a pair of cold cathode tubes 99 and 101, controlled by an inertia switch 102 of any well known construction suitable for the purpose, are arranged to prevent firing of the mine when a sudden shock is received such as is caused by the explosion of a torpedo or another mine within the vicinity of the mine 10 or as the result of a counterrnining operation. A suitable inertia switch is disclosed and claimed in the copending application of Seth. W. Booth for Inertia Switch And Means Controlled Thereby, Ser. No. 484, 854, filed Apr. 28, 1943. The grids 103 and 104 of the tubes 99 and 101 respectively are normally held below firing potential by a condenser 105 which couples the grids to the cathodes.

The operation of the mine is as follows:

When the mine 10 is planted on the bed of a body of water, the hydrostat 44 in response to hydrostatic pressure starts the arming clock 45. The soluble washer 38 begins to dissolve and after a predetermined period of time, it softens sufficiently-to permit the hydrostatic pressure to act upon the diaphragm 34 which inserts the detonator 41into the booster charge 28. After an hour has elapsed, the cam 84 of the arming clock rotates sufficiently in the direction of the arrow to cause the contacts 81 to close and closure thereof connects the positive side of the battery 49 through the lead 106 and the contacts 81 to the lead 107 which is connected to the armature 59 of the polarized relay 57.

In the event that the armature 59 is in engagement with either of the contacts 61 or 62 by reason of the shock caused by launching of the mine, a circuit will be completed from the armature 59 alternatively through either contact 61 lead 108, resistor 65, coil 64 of relay 63, lead 109, lead 1 1 1 and lead 1 12, or contact 62, lead 113, resistor 78, coil 73 of relay 72, lead 114 and lead 1 15, either circuit being completed through lead 116 to the negative side of the battery 49. it is therefore apparent that if contact 61 is in engagement with the armature 59, the relay 63 will be energized and the condenser 66 connected across the coil 64 of the relay will be charged whereas energization of the relay 72 and charging of the condensor 79 connected across the coil 73 of the relay is caused if contact 62 is engaged by the armature 59. In either event, a circuit to the reset coil 58 of the polarized relay 57 is completed, the relay 63 when energized completing a circuit from the positively energized lead 107, through the lead 117, contact 68 now engaged by armature 67, lead 118, lead 119, reset coil 58, to the negatively energized lead 111, and the relay 72 when energized completing a circuit'from the positively energized lead 107, through the lead 117, contact 76 now engaged by armature 74, lead 118, through the reset coil 58 and to the negative side of the battery 49 as previously traced.

The reset coil 58 returns the armature 59 to a position between the contacts 61 and 62 and continues to do so each time the armature 59 engages one or the other of the contacts 61 and 62. When the reset coil 58 disengages the armature 59 from either of its contacts, the respective one of the coils 64 and 73 which was energized by such contact is not immediately deenergized by reason of the charge on the condenser connected thereacross, the condenser 66 requiring approximately one quarter of a second to discharge through the path comprising the resistor 65 and the coil 64 and a similar period being required for the condenser 79 to discharge through the resistor 78 and the coil 73. This delay provides ample time for the reset coil 58 to complete its function of resetting the armature 59 to its normal position.

Energization of either of the relays 63 or 72 during the first 2 hours of operation of the arming clock 45 will not produce any other result than the hereinbefore described reset function by reason of the deenergization of all other circuits in the apparatus at the .arming clock contacts 82 and 83. However, when 2 hours have elapsed, the cam 84 operates the contacts 82 to closed position, with results which will be described hereinafter, the mine not being fully armed at this time as the detonator circuit is open at the contacts 83. After 3 hours, the arming clock closes the contacts 83, it being presumed that within this period the mine laying ship has proceeded to a safe distance from the mine and that the mine has settled into a position on the bed of the body of water from which it will not move whereby the possibility of the mine becoming selfdestructive by reason of its own motion is no longer present. When the contacts 81, 82 and 83 are closed, the arming clock stops and the mine is fully armed.

Let it now be assumed, by way of example, that a vessel having a magnetic signature comprising an elemental portion or characteristic of one polarity followed by an elemental portion or characteristic of the opposite polarity moves within the vicinity of the mine or passes above the mine. As the first portion of the magnetic signature moves into proximate relation with respect to the pickup coil 18, an electromotive force is generated within the pickup coil sufficient to energize the coil 56 of the polarized relay 57 and cause the armature 59 to be moved into engagement with either contact 61 or 62, as the case may be. For the purpose of description, it is assumed that the armature 59 moves into engagement with the contact 61 and, as hereinabove described, the coil 64 of the relay 63 is energized after a slight lapse of time by reason of the delay caused by the charging of the condenser 66 connected across the coil 64.

The coil 64 now attracts both of its armatures 67 and 69, the armature '67 engaging the contact 68 to close a circuit to the reset coil 58 as hereinbefore described. Engagement of the armature 69 with the contact 71 closes a circuit from the positively energized lead 106, to contacts 82 of the arming clock, lead 121, lead 122, armature 69, contact 71, lead 123, resistor 87, condenser 86, lead 124, to the negatively energized lead 1 12 thereby causing the condenser 86 to be charged by the battery 49 through the resistor 87. As previously pointed out, coil 64 maintains its contacts closed for approximately one quarter of a second after the circuit to the coil is opened and this interval provides sufficient time for the condenser 86 to become fully charged. it will be noted that the positively energized lead 123 is also connected to the plate of the cold cathode tube 88 but the grid 96 of this tube is below the firing potential by reason of its connection through the grid resistor 97 to the point 98 which is coupled through the uncharged condenser 89 to the negatively energized lead 116 and the tube 88 therefore does not discharge.

The charge on the condenser 86 raises the potential of the point 95 and as soon as the charging circuit is opened at contact 71 of the relay 63, the condenser 86 begins to discharge through a circuit comprising resistor 94 connected to point 95, grid 93 of the tube 92, the grid-cathode path of the tube 92, which breaks down because the grid is now above the firing voltage of the tube, lead 125, lead 126, detonator 41, lead 127, arming clock contacts 83, to lead 124 connected to the other side of the condenser. The plate circuit of tube 92 is open at contact 77 so that this tube does not fire even though its grid is at firing potential. The resistance of the resistor 94 is of such value that the current flow through the detonator 41 is negligible and will not fire the detonator, the charge on the condenser being dissipated at such a rate as to maintain the grid 93 of the tube 92 at firing potential for a period of approximately 6 seconds. In the event that a second portion of the ships magnetic signature of opposite polarity to the first portion moves into effective relation with the search coil 18 during this period, an electromotive force is generated therein of such polarity as to energize the coil 56 of the polarized relay 57 to cause the armature 59 to engage the contact 62 thereby to energize the coil 73 of the relay 72 through a circuit previously traced. The coil 73 attracts both of its arrnatures 74 and 75, the armature 74 closing a circuit through the contact 76 to the reset coil 58 as traced hereinabove.

Engagement of the armature 75 with the contact 77 closes a circuit through the positively energized lead 121, lead 122, armature 75, contact 77, lead 128, tube 92 which is conducting by reason of the potential maintained on the grid 93 by the condenser 86, lead 125, lead 126, detonator 41, lead 127, contacts 83 of the arming clock, and thence to the negatively energized lead 112 whereby the detonator 41 is fired to explode the mine and damage or sink the ship which has passed a sufficient distance over the mine in the period between the first and second actuations of the polarized relay 57 to present a particularly vulnerable portion of the ship to the effects of the explosion. The condenser 79 and the resistor 78 function to delay separation of the armature 75 from the contact 77 for a quarter of a second thereby to allow ample time for the condenser 85, which is maintained charged by its connection across the battery 49, to discharge into the detonator 41 through the circuit just traced.

It will become apparent from the foregoing description and a study of the circuits that if the polarized relay 57 receives its first actuation by reason of the presence of a vessel in the vicinity of the mine in a direction to engage the armature 59 with the contact 62 and its second actuation engages the armature 59 with the contact 61 within a period of less than 6 seconds after the first actuation, the condenser 89 will be charged by the first actuation thereby to place firing potential on the grid 96 of the tube 88 and the second actuation will place plate voltage on the tube 88 thereby to cause it to discharge the condenser 85 through the detonator 41 and fire the mine.

If at any time during a 6 second period after a first actuation of the relay 57, the relay 57 receives a second actuation in the same direction whereby its armature engages the same contact 61 or 62, as the case may be, as it engaged on its first actuation, the respective condenser 86 or 89 which was charged by the first actuation and has become partly discharged is again recharged thereby renewing the 6 second period in which the relay 57 may receive a reverse actuation which will fire the mine. In the event that any 6 second period expires before a reverse actuation is received, the circuits all return to normal as neither of the grids of the tubes 88 or 92 is at firing potential. Such fortuitous actuations may occur by reason of enemy mine sweeping tactics but unless the precise conditions necessary for firing the mine are duplicated by the enemy, the mine will be practically unsweepable by ordinary magnetic methods.

The circuit for preventing countermine shocks caused deliberately by the enemy or by the explosion of nearby mines from destroying the mine will now be described. Normally the countermine prevention tubes 99 and 101 which are of the cold cathode type are held in a non-firing condition by their respective grids 103 and 104 which are coupled to the negatively energized lead 112 by the lead 129 and the condenser 105. Upon receipt of a countermine shock, the inertia switch 102 rapidly closes momentarily before the shock can operate relays 57, 63 or 72 and connects the condenser across the battery 49 and condenser 85 through the leads 129 and 131. When the inertia switch 102 opens, the condenser 105 begins to discharge through the grids 103 and 104 to the cathodes of the respective tubes 99 and 101 thereby to place these tubes in firing condition. The plate circuit of tube 99 is directly connected across the condenser 86 and if this condenser has a charge on it at the time that the countermine shock is received, the condenser discharges through lead 132 connected to one side thereof, tube 99, lead 133, lead 129, lead 122 and lead 124 to the other side of condenser 86. Similarly, any charge on condenser 89 is discharged through a circuit comprising lead 134 connected to one side of the condenser, tube 101, lead 133 lead 129, lead 112, and lead 116 to the other side of condenser 89. The potential is therefore removed from the grids 96 and 93 of tubes 88 and 92 respectively thereby to prevent the detonator 41 from being fired by discharge of these tubes. The resistance in the circuits of the grids 103 and 104 of the anti-countermine tubes 99 and 101 respectively is of such value as to require substantially 3 seconds to elapse before the condenser 105 discharges sufficiently to reduce the potential on the grids 103 and 104 below the firing potential thereof thereby to maintain the countermine protection for a period sufficient for the countermine shock to subside to a value which will be ineffective to fire the mine. The 3 second period also permits the polarized relay 57 to reset to normal if the countermine shock has moved the armature 59 against either of the magnetic contacts 61 or 62.

Briefly stated in summary, the present invention contemplates the provision of a new and improved mine firing control apparatus adapted to fire a mine when it receives two successive actuations of different polarity from the magnetic signature of a vessel in the vicinity of the mine within a predetermined period and which is constructed of elements having low mass and few moving parts so that the mine firing apparatus is rugged and not subject to damage or injury by the shocks of launching. The invention contemplates the use of cold cathode tubes for this purpose thereby to reduce the drain on the battery to a negligible amount by reason of the fact that these tubes have no filaments and therefore draw no filament current. The invention further contemplates the provision in a mine firing apparatus of a countermine protection means which is simple, rugged and extremely rapid in operation and provides a maximum of protection against countermine shocks however produced.

Although, in accordance with the provisions of the patent statutes, this invention has been described in concrete form with reference to a preferred embodiment thereof which gives satisfactory results, it willbe understood that this form is merely illustrative and that the invention is notlimited thereto since alterations and modifications readily suggest themselves-to persons skilled in the art without departing from the true spirit of this invention or the scope of the annexed claims. 1 Y

The invention herein described and claimed maybe manufactured and used by or for the Government of the United States of. America for governmental purposes without the payment of any royalties thereon or therefor. i

What is claimed as new and desired to be secured by Letters Patent of the UnitedStatesis:

1. In a submarine mine for .damaging'a vessel, the combination of: a mine, electrical means responsive to a condition having. a variable sign and caused by a vessel in motion for producing signals of opposite polarities in accordance with the sign of said condition, a pair of energy storage means, means controlled by said signals for selectively supplying said energy storage means with energy in accordance with the polarities of said signals, and means controlled by one of said energystorage means for firing the. mine when the pair of energy storage means are successively supplied with energy within a predetermined period of time.

2. In a'submarine-mine for damaging a vessel, the combination of: a mine, electrical means responsive to a condition having a, variable sign and causedby a vessel in motionfor producing signals of opposite polarities in accordance. with the 'sign of said condition, a pair of electrical circuits, a condenser in each of said pair of circuits,means controlled by said signalsfor selectively energizing said electrical circuits. and charging said condensers in accordance with the polarities of said signals, and means controlled by the charge on one of said condensers for firing the mine-when-the electrical circuits are energized successively within a predetermined period of time.

3. In a submarine mine for damaging a vessel, the combination of: amine, means responsive to the magnetic field adjacent said vessel for'producingsignals of opposite polaritiesin accordance with the polarity of the magnetic field, a pair of electrical circuits, a condenser in each of said pair of circuits, means controlled by said signals for selectively energizing said electrical circuits and charging said condensers in accordance with the polarities of said signals, and means controlled by the charge on one of said condensers for firing the mine when the electrical circuits are energized successively within a predetermined period of time.

4. In a submarine mine for damaging a vessel, the combination of: a mine, electrical means responsive to a condition having a variable sign and caused by a vessel in motion for producing signals of opposite polarities in accordance with the sign of said condition, a pair of energy storage means, means controlled by said signals for selectively supplying said energy storage means with energy in accordance with the polarities of said signals, and means including electronic tube means controlled by one of said energy storage means for firing the mine when the pair of energy storage means are successively supplied with energy within a predetermined period of time.

5. In a submarine mine for damaging a vessel, the combination of: a mine, means responsive to the magnetic field adjacent said vessel for producing signals of opposite polarities in accordance with the polarity of the magnetic field, a pair of electrical circuits, a condenser in each of said pair of circuits, means controlled by said signals for selectively energizingsaid electrical circuits and means including charging said'condensers in accordance with the polarities of said signals, and. electronic tube means controlled by the charge on one of said condensers for firing the mine when the electrical circuits are energized successively within a predetermined period of time.

6. Ina submarine mine for damaging a vessel, the combination of: amine, means responsive to the 'magnetic field adjacent said vessel for producing signals of opposite polarities in accordance with the polarity of the magnetic field, a pair of electronic tubes each having a grid and a plate circuit, a first circuit including therein the plate circuit of one of said tubes, a second circuit including therein the plate circuit of the other of said electronic tubes, means connecting the grid of said one of said tubes to the second-circuit, means connecting the grid of saidother of said tubes to the first circuit, means controlled by said signals for selectively energizingsaid circuits in accordance with the polarities of the signals, means in each of .said circuitsfor maintaining the gridconnected thereto energized for a predetermined period of time after the respective circuit has beenenergized, and means connected to the plate circuits of said tubes for firing the mine.

7. In the submarine minefor damaging a vessel, the combination of: a mine, means responsive to the magnetic field adjacent said vessel for producing signals of opposite polarities in accordance with the polarity of the magnetic field, a first circuit having a condenser connected therein, an electronic tube having a plate circuit and a grid, a second circuit having the plate circuit of said electronic tube connected therein, a connection from said first circuit to said grid, means controlled by said signals for selectively energizing said circuits in accordance with the polarities of the signals,

and means connected in said second circuit for firing the mine when the second circuit is energized while a voltage above a predetermined value exists across said condenser.

8. In a submarine mine for damaging a vessel, the combination of: a mine, means responsive to the magnetic field adjacent said vessel for producing signals of opposite polarities in accordance with the polarity of the magnetic field, a first circuit having a condenser connected therein, an electronic tube having a plate circuit and a grid, a second circuit having the plate circuit of said electronic tube connected therein, a connection from said first circuit to said grid, means controlled by said signals for selectively energizing said circuits in accordance with the polarities of the signals, means connected in said second circuit for firing the mine when the second circuit is energized while a voltage above a predetermined value exists across said condenser, and means responsive to countermine shocks for shunting said condenser for a predetermined period of time.

9. In a submarine mine for damaging a vessel, the combination of: a mine, means responsive to the magnetic field adjacent said vessel for producing signals of opposite polarities in accordance with the polarity of the magnetic field, a first circuit having a condenser connected therein, an electronic tube having a plate circuit and a grid, a second circuit having the plate circuit of the electronic tube connected therein, a connection from said first circuit to said grid, means controlled by said signals for selectively energizing said circuits in accordance with the polarities of said signals, means connected in said second circuit for firing the mine when the second circuit is energized while a voltage above a predetermined value exists across said condenser, a second electronic tube having a plate circuit and a grid, a shunt circuit connected across said condenser and including the plate circuit of said second tube, and means responsive to countermine shocks for maintaining firing voltage on the grid of the second tube for a predetermined period of time.

10. In a submarine mine for damaging a vessel, the combination of: a mine, means responsive to the magnetic field adjacent said vessel for producing signals of opposite polarities in accordance with the polarity of the magnetic field, a first circuit having a resistor and a condenser in series therein, a first electronic tube having a plate circuit and a grid, a detonator for firing the mine, a series circuit including the plate circuit of the first electronic tube and the detonator connected in parallel with said resistor and condenser, a second circuit having a resistor and a condenser in series therein, a second electronic tube having a plate circuit and a grid, a series circuit including the plate circuit of the second electronic tube and the detonator connected in parallel with the resistor and condenser of the second circuit, a connection from the grid of the second electronic tube to a point between the resistor and condenser of the first circuit, a connection from the grid of the first electronic tube to a point between the resistor and condenser of the second circuit, and means controlled by said signals for selectively energizing said first and second circuits in accordance with the polarities of said signals.

11. In a submarine mine for damaging a vessel, the combination of: a mine, means responsive to the magnetic field adjacent said vessel for producing signals of opposite polarities in accordance with the polarity of the magnetic field, a first circuit having a resistor and a condenser in series therein, a first electronic tube having a plate circuit and a grid, a detonator for firing the mine, a series circuit including the plate circuit of the first electronic tube and the detonator connected in parallel with said resistor and condenser, a second circuit having a resistor and a condenser in series therein, a second electronic tube having a plate circuit and a grid, a series circuit including the plate circuit of the second electronic tube and the detonator connected in parallel with the resistor and condenser of the second circuit, a connection from the grid of the second electronic tube to a point between the resistor and condenser of the first circuit, a connection from the grid of the first electronic tube to a point between the resistor and condenser of the second circuit, means controlled by said signals for selectively energizing said first and second circuits in accordance with the polarities of said signals, and means responsive to countermine shocks for shunting said condensers for a predetermined period of time.

12. In a submarine mine for damaging a vessel, the combination of: a mine, means responsive to the magnetic field adjacent said vessel for producing signals of opposite polarities in accordance with the polarity of the magnetic field, a fu'st circuit having a resistor and a condenser in series therein, a first electronic tube having a plate circuit and a grid, a detonator for firing the mine, a series circuit including the plate circuit of the first electronic tube and the detonator connected in parallel with said resistor and condenser, a second circuit having a resistor and a condenser in series therein, a second electronic tube having a plate circuit and a grid, a series circuit including the plate circuit of the second electronic tube and the detonator connected in parallel with the resistor and condenser of the second circuit, a connection from the grid of the second elec tronic tube to a point between the resistor and condenser of the first circuit, a connection from the grid of the first electronic tube to a point between the resistor and condenser of the second circuit, means controlled by said signals for selectively energizing said first and second circuits in accordance with the polarities of said signals, a pair of electronic devices each having a plate circuit and a grid, a shunt circuit connected across each said condenser and including the plate circuit of one of said devices, and means responsive to countermine shocks for maintaining a firing voltage on the grids of said devices for a predetermined period of time.

13. In a device of the character disclosed, the combination of means for producing signals of opposite polarities, a pair of electrical circuits, a condenser in each of said pair of circuits, means controlled by said signals for selectively energizing said electrical circuits in accordance with the polarities of said signals, an electroresponsive device, and electronic tube means controlled by the charge on one of said condensers for energizing said electroresponsive device when the electrical circuits are energized in succession within a predetermined period of time.

14. In a device of the character disclosed, the combination of a mine, electrical means responsive to a condition having a variable sign and caused by a moving object for producing signals of opposite polarities in accordance with the sign of said condition, a pair of energy storage devices, means controlled by said signals for selectively supplying said energy storage devices with energy in accordance with the polarities of said signals, and means controlled by one of said energy storage devices for firing the mine when the energy storage devices are supplied with energy in succession within a predetermined period of time.

15. In a device of the character disclosed, the combination of a mine, means responsive to the magnetic field adjacent a moving object for producing signals of opposite polarities in accordance with the polarity of the magnetic field, a pair of electrical circuits, a pair of condensers respectively included in each of said circuits, means controlled by said signals for selectively energizing said circuits iii accordance with the polarities of said signals, and means controlled by the charge on one of said condensers for firing the mine when the electrical circuits are energized in succession within a predetermined period of time. I

16. In a device of the character disclosed, the combination of a mine, electrical means responsive to the magnetic field adjacent a moving object for producing signals of opposite polarities in accordance with the polarity of the magnetic field, a pair of electrical circuits, a pair of condensers respectively included in each of said pair of circuits, means controlled by said signals for selectively energizing said electrical circuits in accordance with the polarities of said signals, and means including electronic tube means controlled by the charge on one of said condensers for firing the mine when the electrical circuits are energized in succession within a predetermined period of time.

17. In a submarine mine of the characterdisclosed, the combination of amine firing circuit, a pair of time measuring means each adapted during a predetermined period of time measured thereby to render the other effective to operate said firing circuit thereby to fire the mine when operation of said other of the time measuring means is initiated during said periodof time, means for producing electrical signals of opposite polarities selectively in accordance withthe magnetic sigrnature of a vessel moving with respect thereto, and means controlled by said signals for selectively initiating operation of said time measuring means in accordance with the polarities of the signals. g

18. In a submarine, mine of the character disclosed, the combination of a mine firing circuit, a pair of time measuring means each adapted during a predetermined period of time measured thereby to render the other effective to operate said firing circuit thereby to fire the mine when operation of said other of the time measuring means is initiated during said period of time, means for producing electrical signalsof opposite polarities selectively in accordance with the magrnetic signature of a vessel moving with respect thereto, a second pair of time measuring means individual to said first named time measuring means and adapted upon operation thereof to render the fir'st time measuring means ineffective to control theoperation of each other for the period of time measured by the second time measuring means, and means responsive to countermine shocks for initiating operation of the second pair of time measuring means.

19. In a submarine mine of the character disclosed, the combination of a mine firing circuit, a pair of time measuring means each adapted during a predetermined period of time measured thereby 'to render the other effective to operate said firing circuit thereby to fire the mine when operation of said other of the time measuring means is initiated during said period of time, a

' second pair of time measuring means individual to said first named time measuring means and adapted to initiate operation thereof, means for producing electrical sigrnals of opposite polarities selectively in accordance with the magnetic signature of a vessel moving with respect thereto, and means controlled by said signals for selectively initiating operation of said second pair of time measuring means in accordance with the polarities of the signals.

20. In a submarine mine of the character disclosed, the combination of a mine firing circuit, a pair of time measuring means each adapted during a predetermined period of time measured thereby to render the other effective to operatesaid firing circuit thereby to fire the mine when operation of said other of the time measuring means is initiated during said period of time, a pair of relays individual to said time measuring means and adapted to initiate operation thereof as the relays operate, means for producing electrical signals of opposite polarities selectively in accordance with the magnetic signature of a vessel moving with respect thereto, and means controlled by said signals for selectively operation said relays irn accordance with the polarities of the signals.

21'. In a submarine mine of the charaCter disclosed, the combination of a mine firing circuit, a pair of time measuring means each adapted during a predetermined period of time measured thereby to render the other effective to operate said firing circuit thereby to fire the mine when operation of said other of the time measuring means is initiated during said period of time, a pair of relays individual to said time measuring means and adapted to initiate operation thereof as the relays operate, an induction pickup coil adapted to induce electrical signals of opposite polarities selectively in accordance with the magnetic signature of a vessel moving with respect thereto, a polarized relay connected to said pickup coil and responsive to said signals for selectively operating the relays in accordance with the polarities of the signals, means operated by either of said relays for restoring the polarized relay to an initial unoperated position, a pair of energy storage devices individual to said relays and adapted to have energy stored therein as operation of the relays is initiated, and a pair of circuits individual to said relays for maintaining operation thereof for a predetermined interval of time by the energy stored in said storage devices individual thereto after the polarized relay has been restored to said initial position.

22. In a submarine mine of the character disclosed, the combination of a mine firing circuit, a pair of time measuring means each adapted during a predetermined period of time measured thereby to render the other effective to operate said firing circuit thereby to fire the mine when operation of said other-of the time measuring means is initiated during said period of time, a pair of signal responsive means individual to said first named time measuring means and adapted to initiate operation thereof, means for producing electrical signals of opposite polarities selectively in accordance with the magnetic signature of a vessel moving with respect thereto, means controlled by said sigrnals for suring means ineffective for the period of time measured by the second time measuring means, and means responsive to countermine shocks for initiating operation of the second time measuring means. 

1. In a submarine mine for damaging a vessel, the combination of: a mine, electrical means responsive to a condition having a variable sign and caused by a vessel in motion for producing signals of opposite polarities in accordance with the sign of said condition, a pair of energy storage means, means controlled by said signals for selectively supplying said energy storage means with energy in accordance with the polarities of said signals, and means controlled by one of said energy storage means for firing the mine when the pair of energy storage means are successively supplied with energy within a predetermined period of time.
 2. In a submarine mine for damaging a vessel, the combination of: a mine, electrical means responsive to a condition having a variable sign and caused by a vessel in motion for producing signals of opposite polarities in accordance with the sign of said condition, a pair of electrical circuits, a condenser in each of said pair of circuits, means controlled by said signals for selectively energizing said electrical circuits and charging said condensers in accordance with the polarities of said signals, and means controlled by the charge on one of said condensers for firing the mine when the electrical circuits are energized successively within a predetermined period of time.
 3. In a submarine mine for damaging a vessel, the combination of: a mine, means responsive to the magnetic field adjacent said vessel for producing signals of opposite polarities in accordance with the polarity of the magnetic field, a pair of electrical circuits, a condensEr in each of said pair of circuits, means controlled by said signals for selectively energizing said electrical circuits and charging said condensers in accordance with the polarities of said signals, and means controlled by the charge on one of said condensers for firing the mine when the electrical circuits are energized successively within a predetermined period of time.
 4. In a submarine mine for damaging a vessel, the combination of: a mine, electrical means responsive to a condition having a variable sign and caused by a vessel in motion for producing signals of opposite polarities in accordance with the sign of said condition, a pair of energy storage means, means controlled by said signals for selectively supplying said energy storage means with energy in accordance with the polarities of said signals, and means including electronic tube means controlled by one of said energy storage means for firing the mine when the pair of energy storage means are successively supplied with energy within a predetermined period of time.
 5. In a submarine mine for damaging a vessel, the combination of: a mine, means responsive to the magnetic field adjacent said vessel for producing signals of opposite polarities in accordance with the polarity of the magnetic field, a pair of electrical circuits, a condenser in each of said pair of circuits, means controlled by said signals for selectively energizing said electrical circuits and means including charging said condensers in accordance with the polarities of said signals, and electronic tube means controlled by the charge on one of said condensers for firing the mine when the electrical circuits are energized successively within a predetermined period of time.
 6. In a submarine mine for damaging a vessel, the combination of: a mine, means responsive to the magnetic field adjacent said vessel for producing signals of opposite polarities in accordance with the polarity of the magnetic field, a pair of electronic tubes each having a grid and a plate circuit, a first circuit including therein the plate circuit of one of said tubes, a second circuit including therein the plate circuit of the other of said electronic tubes, means connecting the grid of said one of said tubes to the second circuit, means connecting the grid of said other of said tubes to the first circuit, means controlled by said signals for selectively energizing said circuits in accordance with the polarities of the signals, means in each of said circuits for maintaining the grid connected thereto energized for a predetermined period of time after the respective circuit has been energized, and means connected to the plate circuits of said tubes for firing the mine.
 7. In the submarine mine for damaging a vessel, the combination of: a mine, means responsive to the magnetic field adjacent said vessel for producing signals of opposite polarities in accordance with the polarity of the magnetic field, a first circuit having a condenser connected therein, an electronic tube having a plate circuit and a grid, a second circuit having the plate circuit of said electronic tube connected therein, a connection from said first circuit to said grid, means controlled by said signals for selectively energizing said circuits in accordance with the polarities of the signals, and means connected in said second circuit for firing the mine when the second circuit is energized while a voltage above a predetermined value exists across said condenser.
 8. In a submarine mine for damaging a vessel, the combination of: a mine, means responsive to the magnetic field adjacent said vessel for producing signals of opposite polarities in accordance with the polarity of the magnetic field, a first circuit having a condenser connected therein, an electronic tube having a plate circuit and a grid, a second circuit having the plate circuit of said electronic tube connected therein, a connection from said first circuit to said grid, means controlled by said signals for selectively energizing said ciRcuits in accordance with the polarities of the signals, means connected in said second circuit for firing the mine when the second circuit is energized while a voltage above a predetermined value exists across said condenser, and means responsive to countermine shocks for shunting said condenser for a predetermined period of time.
 9. In a submarine mine for damaging a vessel, the combination of: a mine, means responsive to the magnetic field adjacent said vessel for producing signals of opposite polarities in accordance with the polarity of the magnetic field, a first circuit having a condenser connected therein, an electronic tube having a plate circuit and a grid, a second circuit having the plate circuit of the electronic tube connected therein, a connection from said first circuit to said grid, means controlled by said signals for selectively energizing said circuits in accordance with the polarities of said signals, means connected in said second circuit for firing the mine when the second circuit is energized while a voltage above a predetermined value exists across said condenser, a second electronic tube having a plate circuit and a grid, a shunt circuit connected across said condenser and including the plate circuit of said second tube, and means responsive to countermine shocks for maintaining firing voltage on the grid of the second tube for a predetermined period of time.
 10. In a submarine mine for damaging a vessel, the combination of: a mine, means responsive to the magnetic field adjacent said vessel for producing signals of opposite polarities in accordance with the polarity of the magnetic field, a first circuit having a resistor and a condenser in series therein, a first electronic tube having a plate circuit and a grid, a detonator for firing the mine, a series circuit including the plate circuit of the first electronic tube and the detonator connected in parallel with said resistor and condenser, a second circuit having a resistor and a condenser in series therein, a second electronic tube having a plate circuit and a grid, a series circuit including the plate circuit of the second electronic tube and the detonator connected in parallel with the resistor and condenser of the second circuit, a connection from the grid of the second electronic tube to a point between the resistor and condenser of the first circuit, a connection from the grid of the first electronic tube to a point between the resistor and condenser of the second circuit, and means controlled by said signals for selectively energizing said first and second circuits in accordance with the polarities of said signals.
 11. In a submarine mine for damaging a vessel, the combination of: a mine, means responsive to the magnetic field adjacent said vessel for producing signals of opposite polarities in accordance with the polarity of the magnetic field, a first circuit having a resistor and a condenser in series therein, a first electronic tube having a plate circuit and a grid, a detonator for firing the mine, a series circuit including the plate circuit of the first electronic tube and the detonator connected in parallel with said resistor and condenser, a second circuit having a resistor and a condenser in series therein, a second electronic tube having a plate circuit and a grid, a series circuit including the plate circuit of the second electronic tube and the detonator connected in parallel with the resistor and condenser of the second circuit, a connection from the grid of the second electronic tube to a point between the resistor and condenser of the first circuit, a connection from the grid of the first electronic tube to a point between the resistor and condenser of the second circuit, means controlled by said signals for selectively energizing said first and second circuits in accordance with the polarities of said signals, and means responsive to countermine shocks for shunting said condensers for a predetermined period of time.
 12. In a submarine mine for damaging a vessel, the combination of: a mine, means responsive to the magnetic field adjacent said vessel for producing signals of opposite polarities in accordance with the polarity of the magnetic field, a first circuit having a resistor and a condenser in series therein, a first electronic tube having a plate circuit and a grid, a detonator for firing the mine, a series circuit including the plate circuit of the first electronic tube and the detonator connected in parallel with said resistor and condenser, a second circuit having a resistor and a condenser in series therein, a second electronic tube having a plate circuit and a grid, a series circuit including the plate circuit of the second electronic tube and the detonator connected in parallel with the resistor and condenser of the second circuit, a connection from the grid of the second electronic tube to a point between the resistor and condenser of the first circuit, a connection from the grid of the first electronic tube to a point between the resistor and condenser of the second circuit, means controlled by said signals for selectively energizing said first and second circuits in accordance with the polarities of said signals, a pair of electronic devices each having a plate circuit and a grid, a shunt circuit connected across each said condenser and including the plate circuit of one of said devices, and means responsive to countermine shocks for maintaining a firing voltage on the grids of said devices for a predetermined period of time.
 13. In a device of the character disclosed, the combination of means for producing signals of opposite polarities, a pair of electrical circuits, a condenser in each of said pair of circuits, means controlled by said signals for selectively energizing said electrical circuits in accordance with the polarities of said signals, an electroresponsive device, and electronic tube means controlled by the charge on one of said condensers for energizing said electroresponsive device when the electrical circuits are energized in succession within a predetermined period of time.
 14. In a device of the character disclosed, the combination of a mine, electrical means responsive to a condition having a variable sign and caused by a moving object for producing signals of opposite polarities in accordance with the sign of said condition, a pair of energy storage devices, means controlled by said signals for selectively supplying said energy storage devices with energy in accordance with the polarities of said signals, and means controlled by one of said energy storage devices for firing the mine when the energy storage devices are supplied with energy in succession within a predetermined period of time.
 15. In a device of the character disclosed, the combination of a mine, means responsive to the magnetic field adjacent a moving object for producing signals of opposite polarities in accordance with the polarity of the magnetic field, a pair of electrical circuits, a pair of condensers respectively included in each of said circuits, means controlled by said signals for selectively energizing said circuits in accordance with the polarities of said signals, and means controlled by the charge on one of said condensers for firing the mine when the electrical circuits are energized in succession within a predetermined period of time.
 16. In a device of the character disclosed, the combination of a mine, electrical means responsive to the magnetic field adjacent a moving object for producing signals of opposite polarities in accordance with the polarity of the magnetic field, a pair of electrical circuits, a pair of condensers respectively included in each of said pair of circuits, means controlled by said signals for selectively energizing said electrical circuits in accordance with the polarities of said signals, and means including electronic tube means controlled by the charge on one of said condensers for firing the mine when the electrical circuits are energized in succession within a predetermined period Of time.
 17. In a submarine mine of the character disclosed, the combination of a mine firing circuit, a pair of time measuring means each adapted during a predetermined period of time measured thereby to render the other effective to operate said firing circuit thereby to fire the mine when operation of said other of the time measuring means is initiated during said period of time, means for producing electrical signals of opposite polarities selectively in accordance with the magnetic signature of a vessel moving with respect thereto, and means controlled by said signals for selectively initiating operation of said time measuring means in accordance with the polarities of the signals.
 18. In a submarine mine of the character disclosed, the combination of a mine firing circuit, a pair of time measuring means each adapted during a predetermined period of time measured thereby to render the other effective to operate said firing circuit thereby to fire the mine when operation of said other of the time measuring means is initiated during said period of time, means for producing electrical signals of opposite polarities selectively in accordance with the magnetic signature of a vessel moving with respect thereto, a second pair of time measuring means individual to said first named time measuring means and adapted upon operation thereof to render the first time measuring means ineffective to control the operation of each other for the period of time measured by the second time measuring means, and means responsive to countermine shocks for initiating operation of the second pair of time measuring means.
 19. In a submarine mine of the character disclosed, the combination of a mine firing circuit, a pair of time measuring means each adapted during a predetermined period of time measured thereby to render the other effective to operate said firing circuit thereby to fire the mine when operation of said other of the time measuring means is initiated during said period of time, a second pair of time measuring means individual to said first named time measuring means and adapted to initiate operation thereof, means for producing electrical signals of opposite polarities selectively in accordance with the magnetic signature of a vessel moving with respect thereto, and means controlled by said signals for selectively initiating operation of said second pair of time measuring means in accordance with the polarities of the signals.
 20. In a submarine mine of the character disclosed, the combination of a mine firing circuit, a pair of time measuring means each adapted during a predetermined period of time measured thereby to render the other effective to operate said firing circuit thereby to fire the mine when operation of said other of the time measuring means is initiated during said period of time, a pair of relays individual to said time measuring means and adapted to initiate operation thereof as the relays operate, means for producing electrical signals of opposite polarities selectively in accordance with the magnetic signature of a vessel moving with respect thereto, and means controlled by said signals for selectively operation said relays in accordance with the polarities of the signals.
 21. In a submarine mine of the charaCter disclosed, the combination of a mine firing circuit, a pair of time measuring means each adapted during a predetermined period of time measured thereby to render the other effective to operate said firing circuit thereby to fire the mine when operation of said other of the time measuring means is initiated during said period of time, a pair of relays individual to said time measuring means and adapted to initiate operation thereof as the relays operate, an induction pickup coil adapted to induce electrical signals of opposite polarities selectively in accordance with the magnetic signature of a vessel moving with respect thereto, a polarized relay connected to said pickup coil and responsive to said signals for selectively operating the relays in accordance wIth the polarities of the signals, means operated by either of said relays for restoring the polarized relay to an initial unoperated position, a pair of energy storage devices individual to said relays and adapted to have energy stored therein as operation of the relays is initiated, and a pair of circuits individual to said relays for maintaining operation thereof for a predetermined interval of time by the energy stored in said storage devices individual thereto after the polarized relay has been restored to said initial position.
 22. In a submarine mine of the character disclosed, the combination of a mine firing circuit, a pair of time measuring means each adapted during a predetermined period of time measured thereby to render the other effective to operate said firing circuit thereby to fire the mine when operation of said other of the time measuring means is initiated during said period of time, a pair of signal responsive means individual to said first named time measuring means and adapted to initiate operation thereof, means for producing electrical signals of opposite polarities selectively in accordance with the magnetic signature of a vessel moving with respect thereto, means controlled by said signals for selectively initiating operation of said signal responsive means in accordance with the polarities of the signals, and a second time measuring means connected to said first named time measuring means and adapted upon operation thereof to render the first named time measuring means ineffective for the period of time measured by the second time measuring means, and means responsive to countermine shocks for initiating operation of the second time measuring means. 